1. Field of the Invention
The present invention relates to a controller and a switching converter, and more particularly to an analog variable-frequency controller and the switching converter therewith.
2. Description of the Related Art
Battery-powered electronic devices, such as cell phones, digital personal assistants etc., often require highly efficient DC-DC switching converters to convert battery voltage to the required operating voltage with voltage regulation. This type of converters needs to work over wide load current range. Therefore, it is very important to maintain high power efficiency in such a wide range.
A pulse frequency modulation (PFM) of a prior art may be used to increase the power efficiency by varying the switching frequency. However, pulse frequency modulation can only improve the light-load power efficiency but not the heavy-load power efficiency. An adaptive frequency control method of another prior art can adaptively select the switching frequency for a given load to minimize the input power to increase the power efficiency. Referring to FIG. 1a, by adapting the switching frequency based on the load current, an optimized power efficiency, as shown in FIG. 1b, is obtained. However, this method is implemented by an analog to digital converter to calculate the input voltage/current and a digital control circuit to select the switching frequency, which leads to a complicated circuit of high implementation cost and larger controller power-loss.
In summary, it is highly desirable that a controller with a more simple circuit and without an analog to digital converter is capable of generating a variable-frequency control signal depending on system load to achieve the optimized power efficiency of a switching converter.